Test methods of this kind are known from DE-OS No. 27 20 865.
The systems suitable for performing the method can be used, for example, for the non-destructive testing of materials where the workpieces are irradiated by X-rays, the intercepted X-rays being converted into visible light by an image converter.
The existing systems, however, often have an insufficient signal-to-noise ratio. The noise is caused mostly by electrical noise as well as by quantum noise.
It is also known that by repetition of television images the noise can be reduced inversely proportionally to the root of the number of repeated images. This method, however, has the drawback that it can be used only for stationary objects which occupy a fixed position in the television image.
Moreover, not all interference effects are eliminated by this method. For example, a phase structure normally present in the camera tube is not suppressed, because it recurs in each image and is not subject to statistical fluctuations.